Patent GB-745185-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B59/04
Filed: 1953-09-24
Abstract: 745,185. Sewing-machines. PFAFF AKT.- GES., G. M. Sept. 24, 1953 [Sept. 24, 1952], No. 26278/53. Addition to 721,975. Class 112. Stitch-forming devices.-Means for automatically exchanging a full bobbin-case for an empty one in a rotary lock-stitch loop-taker comprises a pair of gripping devices 44, 45, Fig. 1, on a carrier 40 mounted on a shaft 3 parallel to the loop-taker shaft L, the former shaft being slidable and rotatable under the control of a pin thereon engaging slots or recesses in a sleeve surrounding the shaft. In the arrangement seen from below in Fig. 1, the shaft 3 is slidable in a bracket 1 and in a sleeve 4 fixed to a bracket 2, the sleeve having secured within it bushings 5, 6, Fig. 2, formed with pairs of grooves 19, 20 to receive opposed pins 21 on the shaft; each groove 19 communicates with the groove 20 on the opposite side by a helical slot 26 formed by the opposed ends of the bushings 5, 6. A leaf spring 24 fixed in each groove 20 allows the pin 21 to ride over it in moving to the right, but deflects it into the slot 26 on the return movement, so that the shaft 3 makes a half-revolution on each leftward movement only. The bushing 5 has a lug 7 which lies between two screws 15, Fig. 1, whereby the bushing can be adjusted angularly to align the grippers accurately with the loop-taker. The shaft 3 is reciprocated when required by a lever (not shown) engaging a pin 39 on a member 36 sliding on a fixed rod 33 and formed with a fork 37 engaging between a pair of collars 28 fixed on the shaft; a spring 29 normally holds the shaft in its left-hand position. Full bobbin cases are stored in a magazine 70 which is held in place by a hinged member 102 with a spring catch 115; they are threaded on a non-circular rod which is fixed to the end-cap 72 of the magazine, the cap being located angularly by projections engaging notches in the body 70 so that the bobbin-cases are correctly orientated to be picked up by the grippers. A pusher fitting in the magazine 70 and spring-pressed to the left urges the bobbin-cases towards the gripper, the bobbin-case at the free end and the next one being secured by their latches engaging notches in the rod on which they slide, in the same manner as they would be in the looptaker ; the bobbin-case next to be used is thus free from the pressure of the spring. The end of the pusher is formed with a similar latch by which it can be held back while the magazine is loaded. Each gripping device, Fig. 7, comprises a cylindrical body 59 secured in a bore in the carrier 40 and having pivoted to it a member 51 with a fork 61 and with a further hook member 50 pivoted to it, the member 50 being pressed to the engaging position by a spring 56 and having a releasing pin 55; the member 50 of the gripper 44 for the empty bobbin-case has no projection 53. The member 51 is held in its engaging or disengaging position by a sliding detent 48, pressed by a leaf-spring 47 (Fig. 1), with either of two notches in the member 51. In order to exchange bobbin-cases, the operating lever of the device is moved and released twice. On the first movement of the shaft 3 to the right, the gripper 44 engages the empty bobbincase B in the loop-taker and the gripper 45 engages the full bobbin-case presented at the end of the magazine 70. On release, the shaft 3 moves to the left and makes half a turn, thus withdrawing both bobbin-cases and carrying the full one to a position in line with the looptaker; the empty one is dropped during this rotation, its gripper 44 being released by engagement of its pin 55 with an adjustably fixed member 68, and the gripper member 51 being held in its disengaged position by the detent 48. On the second movement of the shaft 3 to the right, the full bobbin-case is inserted in the loop-taker, the gripper 45 being released by engagement of its nose 53 with the loop-taker body, while the gripper 44 makes an idle movement. On release, the shaft moves to the left and turns the carrier 40 further to its original position ; during this half-revolution a cam 32 which is rotated by the shaft 3 but takes no part in its sliding movement, engages a lever pivoted on the magazine 70 to depress the latch of the next bobbin-case in the magazine, thus freeing it from the notch in the magazine guide-rod so that it moves to the end of the magazine while the succeeding bobbin moves to engage the notch.